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 Post subject: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sat 16, 2016 12:52 am 
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I'm running a restored Bogen DB 130. I would like to hook up two speakers and run both (speaker selector in "AB" position). My question is if the speakers are 8 ohm impedance do I leave the selector switch on the back of the amp in the 8 ohm position or do I need to switch it to 16 ohm? Theres probably an easy answer to this question but I don't have the manual for this amp and I don't know how the speaker wiring is set up inside it.

On a side note I would like to run a set of 6FW5 tubes but will need to adjust the screen voltage for them. I have yet to find the instructions for the procedure.

Thanks for any assistance :D .

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sat 16, 2016 5:23 am 
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Quote:
My question is if the speakers are 8 ohm impedance do I leave the selector switch on the back of the amp in the 8 ohm position or do I need to switch it to 16 ohm?


if you wire the speakers in parallel, they now become a 4 ohm load on the amp. does the switch have the provision for selecting 4 ohms ? if it does, put the switch on 4 ohms and hook up the paralleled 8 ohm speakers which is now a 4 ohm load on the amp.

if there is no selection for 4 ohms, there is another way to skin the cat.

put the two 8 ohm speakers in series. they both will now be a 16 ohm load for the amp to see. put the switch on the amplifier to 16 ohms and the amp will be happy.

steve

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sat 16, 2016 3:16 pm 
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I should also note that even though this is a mono amplifier there are two choices of speaker outs. Theres "Common", "A" and "B" connection points and the speaker selector has an "AB" position. If there was just one out then you would be quite correct 'Rabbit (not saying your wrong either :) ). I suppose I could just use "A" and wire my speakers in series as you said and call it done.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sat 16, 2016 8:57 pm 
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make the impedance of the speaker load match the setting of the amp for best results.

steve

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sat 16, 2016 9:18 pm 
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I wired a pair of 8 ohm cabinets in series to "A" and set the impedance switch to 16 ohm. Ran at moderate volume for a couple hours and its nice and happy.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Sun 17, 2016 3:34 am 
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8 + 8 in series = 16 ohms >> switch to 16 ohms = Winner

:D

steve

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Mon 18, 2016 1:39 am 
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I have the actual DB130 instruction manual, schematic, and two amplifiers. The speaker selector switch takes care of parallel speaker impedance.

Since you have two 8 ohm speakers, connect one to A & Com, other to B & Com, and set impedance for 8 ohms.

For two 16 ohm speakers, same but set impedance for 16 ohms.

For a single 4 ohm speaker, connect to A or B and Com, impedance to 8 ohms, but set selector to AB.

This means the A-B-AB speaker switch moves the impedance from 16 to 8, or 8 to 4, when in position AB to handle parallel speakers. It could not be easier for the user.

6FW5 is just an uprated 6AV5, and far more rugged. I have four of them in a Bogen LX60 Public Address Amplifier, (similar circuit but bigger) and it is loud enough to peel the paint off the walls, along with outstanding sound quality. Same adjustment as the 6AV5.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Mon 18, 2016 2:59 pm 
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Thanks for the input :D . So the 6FW5 is a drop in, no adjustment needed swap for the 6AV5? I'll change around the speaker arrangement as well. Thanks again :D .

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Mon 18, 2016 5:19 pm 
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badwaxcaps wrote:
Thanks for the input :D . So the 6FW5 is a drop in, no adjustment needed swap for the 6AV5? I'll change around the speaker arrangement as well. Thanks again :D .


They recommended Output Stage Balancing any time a 6AV5 is replaced:

1. Using a screwdriver, turn the Volt Reg Adj and the Bal Adj controls full counterclockwise.

2. Rotate the Volume control full CCW, turn Power on, allow 4 minutes warmup.

3. Remove the two shorting straps from the Bal Mon strip and connect the probes of a DC meter to TP 1 (+) and 2 (-)

4. Adjust the Volt Reg Adj control for a 1.5 volt meter reading.

5. Transfer the negative probe from TP 2 to TP3 annd adjust the BAL ADJ control for a meter reading of Zero Volts.

6. Replace the two shorting straps on the BAL MON terminal strip (Short 1 & 2; Short 2 & 3)

It mentions that you can get approximate balance by lining up the slots of the two controls with the indicator marks adjacent to each of the control adjustment holes.

I will add that with today's higher line voltage, the Volt Adj will probably be set back from before. The screen voltage is regulated by the 6CG7, and that is set by the Volt Adj pot.
My big PA amp had a 125 volt tap on its primary, but these DB130 do not, and a voltage bucking transformer would be a good addition. Note that this amplifier runs close to class B, low idle current, so a dropping resistor in the primary would not work well due to the widely varying plate current.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 12:00 am 
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Thank you very much for the info :D . It'll come very much in handy when the new tubes get here. I'm trying to find a pair that rather well matched.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 3:42 am 
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badwaxcaps wrote:
Thank you very much for the info :D . It'll come very much in handy when the new tubes get here. I'm trying to find a pair that rather well matched.


I had to look at the internal construction, there were two different types of 6FW5, and when in parallel pairs, the one that looked different did not conduct any current! (There were test points on the four cathode resistors). You can open the jumpers and compare screws 1 & 3 with a scope to see how the tubes compare with a signal. The Bal Adj shifts the grid bias to get the idle current equal, but that doesn't help if the tubes are different construction and different gain.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 8:38 am 
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I have not ordered them yet so thanks for the additional info :D . I'll be sure to get a pair with matching internals and specs. Any suggestions on particular vendors to look in to?

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 2:45 pm 
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They were $3 each when I bought mine in the 1990's, so I bought eight, to have spares. I ended up swapping around to get a quad set that worked equally in the LX60, so be sure to order a bunch. Public-address amps work harder than home Hi-Fi sets, but 6FW5 are designed for sweep service and don't even seem to clip at full blast. I used an HH Scott 40 watt amplifier with 6CA7 tubes for a second speaker, and the Scott was straining and distorting.
I tried my DB130 for television sound, and on a Sci-fi movie the deep bass of sound effect weapon blasts was startlingly strong.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 8:15 pm 
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I just realized the power tubes in this amp are 6AU5's...

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Jul Tue 19, 2016 10:43 pm 
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badwaxcaps wrote:
I just realized the power tubes in this amp are 6AU5's...


6AU5 is almost the same as 6AV5, both rated for 550 volts, but the 6FW5 is rated for 770 volts so it is much better able to handle the 605 volts plate voltage used in the DB130.

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 Post subject: Re: Question on Bogen DB 130 speaker hook up and impedance.
PostPosted: Feb Sun 04, 2018 9:27 pm 
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Bikenswim or anyone....Looking for scans of or a printed copy of the Bogen db130 amp user manual. I bought one used but "refurbished" or gone through for daily use. Want to use the system for daily listening. Will be using a 1959 JBL C36 speaker...16 ohm drivers N2400 crossover...hope it's compatible. Thanks ...Would appreciate link to a digital copy if one is out there


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